No abstract

Over the last decade, there has been increasing interest in transferring the research advances in radiofrequency (RF) rectifiers, the quintessential element of the chip in the RF identification (RFID) tags, obtained on rigid substrates onto plastic (flexible) substrates. The growing demand for flexible RFID tags, wireless communications applications and wireless energy harvesting systems that can be produced at a low-cost is a key driver for this technology push. In this topical review, we summarise recent progress and status of flexible RF diodes and rectifying circuits, with specific focus on materials and device processing aspects. To this end, different families of materials (e.g. flexible silicon, metal oxides, organic and carbon nanomaterials), manufacturing processes (e.g. vacuum and solution processing) and device architectures (diodes and transistors) are compared. Although emphasis is placed on performance, functionality, mechanical flexibility and operating stability, the various bottlenecks associated with each technology are also addressed. Finally, we present our outlook on the commercialisation potential and on the positioning of each material class in the RF electronics landscape based on the findings summarised herein. It is beyond doubt that the field of flexible high and ultra-high frequency rectifiers and electronics as a whole will continue to be an active area of research over the coming years.

Air‐stable semiconducting inks suitable for complementary logic are key to create low‐power printed integrated circuits (ICs). High‐performance printable electronic inks with 2D materials have the potential to enable the next generation of high performance low‐cost printed digital electronics. Here, the authors demonstrate air‐stable, low voltage (<5 V) operation of inkjet‐printed n‐type molybdenum disulfide (MoS2), and p‐type indacenodithiophene‐co‐benzothiadiazole (IDT‐BT) field‐effect transistors (FETs), estimating an average switching time of τMoS2 ≈ 4.1 μs for the MoS2 FETs. They achieve this by engineering high‐quality MoS2 and air‐stable IDT‐BT inks suitable for inkjet‐printing complementary pairs of n‐type MoS2 and p‐type IDT‐BT FETs. They then integrate MoS2 and IDT‐BT FETs to realize inkjet‐printed complementary logic inverters with a voltage gain |Av| ≈ 4 when in resistive load configuration and |Av| ≈ 1.4 in complementary configuration. These results represent a key enabling step towards ubiquitous long‐term stable, low‐cost printed digital ICs.

Large-area manufacturing of flexible nanoscale electronics has long been sought by the printed electronics industry. However, the lack of a robust, reliable, high throughput and low-cost technique that is capable of delivering high-performance functional devices has hitherto hindered commercial exploitation. Herein we report on the extensive range of capabilities presented by adhesion lithography (a-Lith), an innovative patterning technique for the fabrication of coplanar nanogap electrodes with arbitrarily large aspect ratio. We use this technique to fabricate a plethora of nanoscale electronic devices based on symmetric and asymmetric coplanar electrodes separated by a nanogap < 15 nm. We show that functional devices including self-aligned-gate transistors, radio frequency diodes and rectifying circuits, multi-colour organic light-emitting nanodiodes and multilevel non-volatile memory devices, can be fabricated in a facile manner with minimum process complexity on a range of substrates. The compatibility of the formed nanogap electrodes with a wide range of solution processable semiconductors and substrate materials renders a-Lith highly attractive for the manufacturing of large-area nanoscale opto/electronics on arbitrary size and shape substrates.

The growth mechanism of indium oxide (In 2 O 3 ) layers processed via spray pyrolysis of an aqueous precursor solution in the temperature range of 100-300 °C and the impact on their electron transporting properties are studied. Analysis of the droplet impingement sites on the substrate's surface as a function of its temperature reveals that Leidenfrost effect dominated boiling plays a crucial role in the growth of smooth, continuous, and highly crystalline In 2 O 3 layers via a vapor phase-like process. By careful optimization of the precursor formulation, deposition conditions, and choice of substrate, this effect is exploited and ultrathin and exceptionally smooth layers of In 2 O 3 are grown over large area substrates at temperatures as low as 252 °C. Thin-film transistors (TFTs) fabricated using these optimized In 2 O 3 layers exhibit superior electron transport characteristics with the electron mobility reaching up to 40 cm 2 V −1 s −1 , a value amongst the highest reported to date for solution-processed In 2 O 3 TFTs. The present work contributes enormously to the basic understanding of spray pyrolysis and highlights its tremendous potential for large-volume manufacturing of high-performance metal oxide thin-film transistor electronics.